Many wet processes are performed in semiconductor fabrication. These processes may include electrochemical plating (ECP), electrochemical mechanical polishing (ECMP), spin-coating, cleaning and etching, to name some examples. Hence, many apparatuses have been designed and are currently available for wet processing wafers and other substrates.
A typical wet processing apparatus may include a process cell for confining a process chemical and a carrier head that holds a wafer within the cell so that it may be treated by the chemical contained in or introduced into the cell. In wet processing apparatuses, (e.g., ECP and ECMP apparatuses), the cell includes an anode of a fixed shape. During processing, the anode is typically located a certain distance from the wafer such that a three-dimensional space is defined between the anode and wafer. The chemical (e.g., an electrolyte containing ions of metal to be deposited on the substrate) disposed in or subsequently introduced into the space between the anode and the wafer, is subjected to an electric field that is generated in the chemical by applying an electric potential between the anode and the wafer which operates as a cathode. In the case of and electrolyte chemical, the electric field generated in the electrolyte causes the metal ions in the electrolyte to be deposited on the wafer, thereby forming a metal layer thereon.
One drawback of these wet processing apparatuses is that the height of the three-dimensional space between the anode and the wafer is the same across the entire wafer, consequently, the electrical field density distribution within the chemical cannot be controlled or varied. As semiconductor wafers increase in size and minimum device feature size decreases, the inability to control the electrical field density distribution within the chemical in the space will lead to device characteristics across the wafer that are undesired or which can not be selectively varied.
Accordingly, improved wet processing apparatuses and methods are needed which enable the density distribution within the chemical in the three-dimensional space between the anode and the wafer to be controlled.